Polymer electrolyte membranes are useful in electrochemical devices such as batteries and fuel cells because they function as electrolyte and separator. Such membranes may be readily fabricated as thin flexible films which can be incorporated into cells of variable shape.
Perfluorinated hydrocarbon sulfonate ionomers, such as NAFION® by DuPont or analogous Dow perfluorinated polymers, are currently being used as polymer electrolytes for fuel cells. Such prior membranes, however, have some severe limitations for use in both hydrogen/air fuel cells and liquid feed direct methanol fuel cells.
An exemplar of a fuel cell which incorporates such a prior membrane is U.S. Pat. No. 5,759,712 to Hockaday which shows a surface replica fuel cell for a micro fuel cell electrical power pack. The disclosed micro fuel cell electrical power pack is configured to power a cellular phone. An evaporative manifold is provided for wicking out fuel from a fuel tank bottle.
What is needed, among other things, is a fuel cell assembly having a removable fuel cartridge capable of maintaining a positive pressure to facilitate flow of fuel from the cartridge to the fuel cell assembly.
Furthermore, fuel cell systems for powering electronic devices have not heretofore achieved any measure of commercial success, at least in part because of the difficulties associated with (i) providing a fuel cell in a physical package that would be adopted by device manufactures, particularly for mobile telephone applications, and (ii) achieving and regulating required power (voltage and current) levels with acceptable reliability, consistency, and safety.
These limitations have been particularly problematic where the power requirements of the electronic device tend to vary at different phases of operation. For example, in a mobile cellular phone, the power requirements are quite modest for standby operation while waiting to receive a call, increase when receiving the call, and then raise tremendously while in a transmit mode. These and other circumstances require or benefit from a interface and control circuit that permits connection of a fuel cell based power supply to electronic devices and advantageously connection and interchangeable use or retrofit of fuel cell based power supplies or systems to existing electronic devices.
What is needed, among other things, is an interface circuit adapted to control and regulate power draw and charge/discharge from both the fuel cell and the battery to maintain operation within predefined voltage, current, and power ranges and to maintain safety when either or both flammable fluids associated with operation of the fuel cell and explosive materials associated with the operation of Lithium-Ion batteries are present.